Picture this:

You have three devices at home, A, B and C. Only device A have Internet connection and can connect to public Yggdrasil node. B can connect only to A and C. C can connect only to B. Have Yggdrasil installed on all of them (and tell Yggdrasil about the peers), all devices would have access to full Yggdrasil network.

And? How is that novel? I read the site as saying the have a new, and better solution to how to do internet scale routing (in an overlay network, but that did not seem like a critical aspect)